Transmission line pulse generator



Oct. 30, 1956 R. D. DROSD 2,769,101

TRANSMISSON LINE PULSE GENERATOR Filed July 29, 1955 s I 2 PRIOR ART INVEETOR R. D. DROSD United States Patent TRANSMISSION LINE PULSE GENERATOR Ralph D. Drosd, Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Navy Application July 29, 1955!, Serial No. 525,408

Claims. (Cl. 307108) (Granted under Title 35, U. S. Code (1952.), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to impulse generators and more particularly to a transmission line arrangement for generating square pulses of preassigned duration.

For many purposes, especially in X-ray systems, it has been found desirable to discharge high voltage pulses of rectangular wave form and preassigned duration across a load. Heretofore, this has conveniently been obtained by discharging a transmission line into a load connected across the transmission line by means of a switch in series with the load. However, it has been found that this arrangement has many disadvantages. For example, the voltage of the pulse can be only half of the voltage to which the line is charged if the load impedance matches the line impedance; and, if the load impedance is increased, the pulse voltage increases but with the result that multiple pulses are obtained instead of a single pulse. Also, due to the location of the switch with respect to the load and supply source, the switch invariably tends to introduce undesirable capacity, inductance and resistance effects in the load circuit, and in addition, is required to hold off twice the pulse voltage. Furthermore, the only way to increase the pulse voltage is to increase the line voltage thereby requiring a power source which must be capable of producing higher voltages and which, in turn, increases the problem of high voltage leakage insulation.

The general purpose of this invention is to provide transmission line arrangements for producing high voltage pulses of rectangular wave form and which avoids the above disadvantages of prior art arrangements.

In accordance with the invention, the phenomenon of creating a magnetic field from a collapsing electrostatic field in a transmission line arrangement of the reflecting line type is employed to develop a square wave impulse across a load. The present invention contemplates the provision of a pair of matched transmission line sections or networks energized from a source of direct current to develop an electrostatic field therein and a switch for collapsing the electrostatic field, the collapse thereof creating in the sections a magnetic field of which the circulating currents establish a potential difference across a matched load which interconnects the sections in tandem so as to form a composite line to thereby produce in the load a voltage surge of uniform amplitude and preassigned duration.

With the foregoing in mind, it is an important object of the present invention to provide a new and improved transmission line square wave pulse generator.

It is another object of the present invention to provide a transmission line generator for producing pulses of rectangular wave form and equal to the charging voltage.

Another object is to provide, in a transmission line arrangement adaptable to have an electrostatic field develice oped therein for producing a pulse across a load, a switch for collapsing the electrostatic field and arranged as to be isolated from the load to thereby eliminate the possibility of introducing undesirable reactance and resistance effects in the load.

A further object is to provide transmission line arrangements for producing square pulses wherein the voltage level of the pulses may be increased without increasing the charging voltage.

Another further object is to obtain from a fixed voltage power source, pulses having an amplitude which is a multiple of the power source voltage without introducing extraneous or spurious pulses.

A still further object is to provide pulse generating transmission line arrangements wherein the voltage amplitude of the pulses is a multiple of the voltage from a direct current source connected to energize the transmission lines.

A still another object is to provide a transmission line voltage doubler for generating square waves from a source of direct current.

Another further object resides in the provision of a voltage tripler arrangement comprising a pair of transmission line sections for generating square wave pulses from a source of direct current.

A primary object of the invention is the provision of a pair of matched transmission line sections interconnected by a load circuit including a load having twice the impedance of one of the line sections, a direct current source for applying a charging potential to the line sections, and a switch operable to present a discharge path for the line sections whereby a square wave pulse equal to the charging potential is produced across the load.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

Figure 1 illustrates a prior art transmission line arrangement for generating square wave pulses;

Figure 2 illustrates schematically the basic embodiment of the invention;

Figure 3 is a voltage doubler incorporating the basic concept of the invention; and

Figure 4 is directed to a voltage tripler arranged in accordance with the basic concept of the invention.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown a prior art arrangement in Fig. 1 which comprises a coaxial transmission line having inner and outer conductors 18 and 19, respectively, connected across a source of direct current Es through charging resistor 10 and conductors 11 and 12. A load Z is connected in series with switch S1, closure of switch S1 connecting the load across conductors 18 and 19.

In operation, with switch S1 open the conductors 18 and 19 function as the electrodes of a capacitor, and an electrostatic field having a potential difference equal to the voltage of source Es is built up in the coaxial line. The time for completely charging up the electrostatic field between conductors 18 and 19 is determined by the time constant of charging resistor 10 and the capacity effect between conductors 18 and 19. Upon closure of switch S1 and under matched load conditions, the electrostatic field discharges through load Z, delivering a pulse thereacross which is half the voltage to which the line is charged. Under mismatched load conditions, a plurality of pulses are obtained. This arrangement has many undesirable features including, among others, extraneous reactance and resistance effects and the necessity of increasing the line voltage in order to increase the pulse voltage.

Referring now to Fig. 2, which illustrates the basic concept of the invention, there is shown a pair of coaxial transmission line sections, indicated generally as Z1 and Z2, connected in tandem with a load Z1 therebetween. The lines are of equal electrical length and have the same characteristic impedance, and the load Z1 has an impedance equal to twice the impedance of one of the lines (Zz=2Z1=2Z2). This is a critical limitation which, if not observed, will result in a plurality of pulses. A source of direct current Es, such for example as a battery, has the positive end thereof connected through charging resistor 19 and lead ll to inner conductor 2% of coaxial line Z1, and the negative end thereof connected through lead 12 to outer conductor 2; of line Z1. The inner conductor 23 of line Z is connected in series with load Z1 and inner conductor 20, the outer conductors 21 and 24 being serially connected by lead 22. A normally open switch S1 is connected across inner conductor 29 and outer conductor 21.

Although the load Z1 is shown in series with the center conductors, it could also be placed in series with the outer conductors as indicated at X. The switch S1 may be of any type such as a snap switch, thyratron, or a spark-gap type switch. The load Z1 may be a resistance or any other device which has a reasonably constant impedance such, for example, as X-ray tubes or flash lamps, and the source Es may be variable so that any desirable voltage value may be utilized. The transmission lines, though shown and described as coaxial lines, may be parallel wire lines or lumped parameter lines. Although the inner conductors and outer conductors are connected to the positive and negative terminals, respectively, of the source Es, it is to be understood that the polarities may be reversed.

In the operation of Fig. 2 and with switch S1 open, the source Es charges lines Z1 and Z2 up to the voltage of source Es in a period of time determined by the time constant of charging resistor and the capacity effects of lines Z1 and Z2. The parameters of resistor 19 and capacity effects of the coaxial lines are so selected that the time for charging the coaxial lines is relatively much greater than the time for discharging the lines. Upon the lines Z1 and Z2 being fully charged and since resistor is is relatively much greater than the line or load impedances, resistor 10 presents a virtual open circuit to source Es thereby isolating the transmission lines from source Es during the period of discharge; and since both ends of load Z1 are at the same potential, there is no discharge through load Z1. Charging of lines Z1 and Z2 develops an electrostatic field between the inner and outer conductors thereof having a potential difference equal to the voltage of source Es, this electrostatic field being retained as long as switch S1 remains open. At any time that a pulse is desired to appear across load Z1, switch S1 is closed.

Upon closure of switch S1, the inner and outer conductors of lines Z1 and Z2 are connected together through leads 11, 14 and 12 and the developed electrostatic field' collapses. As the electrostatic field collapses, a magnetic field is set up. in coaxial line Z1, and, a circulating current wave of zero voltage travels from left to right in line Z1 until it reaches the load Z1. At this point, a voltage equal to half the charging voltage of source Es and of opposite polarity appears at the load end connected to conductor 20. Meanwhile, the same phenomenon occurs in line Z2 with the exception that the voltage presented to its respective end of the load, is of the same polarity as the charging voltage of source Es. This results in a voltage difierence across the load Z1, the voltage diflference being equal to the charging voltage of source Es; and since the load impedance matches the total line impedance, the lines discharge across load Z1 to produce a single square wave pulse having a magnitude equal to the charging voltage and a duration equal to twice the electrical length of one of the lines.

Referring now to Fig. 3, there is shown a voltage doubler circuit constructed in accordance with the present invention and comprises a pair of transmission line sections, indicated generally as A and B, connected in tandem with a load Z1 interconnected therebetween. Sections A and B each consist of a pair of coaxial lines Z3, Z5 and Z4, Z6, respectively, the lines Z3, Z4, Z5 and Z6 being of equal electrical length and having the same characteristic impedance. The outer conductor 26 of line Z2 is serially connected with outer conductor 2? of line Z4 through lead 27, and inner conductor 25 of line Z3 is connected in series with inner conductor 33 of line Zs through lead 35. Similarly, the inner conductor 3% of line Z5 is connected in series with load 2'1 and inner conductor 28 of line Z4, and outer conductor 31 is connected in series with outer conductor 34 by means of lead 32. The inner conductors of sections A and B are connected to the positive terminal of source Es through leads 15, 14, l1 and charging resistor 10. From this arrangement, it is apparent that a pair of series paths each consisting of two inner conductors in series, are connected to the positive terminal of source Es.

The outer conductor 26 is connected through lead 13 to outer conductor 31 which in turn is connected to outer conductor 34 through lead 32 and to the negative terminal of source Es through lead 12 thereby connecting two series paths to the negative terminal of source Es. A switch S1 is connected across conductors 11 and 12 and therefore is, in eitect, connected between the pair of inner conductor series paths and the pair of outer conductor series paths to thereby connect the inner and outer conductors upon closurethereof. Although load Z1 is connected serially with conductors 23 and 30, it may be serially inserted in either'one of leads 27, 35, or 32, as indicated by the X marks.

In the operation of Fig. 3 and with switch S1 open, the transmission lines Z3, Z4, Z5 and Z6 are charged by source Es to develop an electrostatic field between their respective inner and outer conductors, as explained with respect to Fig. 2. To produce a pulse across load Z1, closure of switch S1 collapses the electrostatic held and a magnetic field is set up having circulating currents of zero voltage in each transmission line. The circulating currents are propagated through each transmission line toward load 2'1, and upon reaching the load Zi, their efiects are cumulative, as described with respect to Fig. 2, to establish across load Z1 a potential diiference equal to twice the charging voltage of load Z'1 thereby produc ing a single square wave pulse having a magnitude equal to twice the charging voltage and a duration equal to twice the electrical length of one of the transmission lines.

Figure 4 illustrates a voltage tripler circuit arranged in accordance with the invention and comprises a pair of transmission line sections C and D interconnected in tandem by means of matched load Z1, section C consisting of coaxial lines Z7, Z9 and Z11 and section D consist ing of coaxial lines 28, Z10 and Z12, the coaxial lines Z7 to Z12 being of the same electrical length and characteristic impedance. The load Z1 is selected to have an impedance equal to the sum total of lines Z7 to Z12 or six times the impedance of each coaxial line.

Three series paths of inner conductors, namely inner conductors 36 and 39 connected by lead 38 forming a first path, inner conductors 41 and 51 with lead 47 forming a second path, and inner conductors 48 and 45 with load Z"1 forming the third path, are connected through leads ll, 16, 17 and 14- to a common terminal 66 which is. connectedto the positive terminal of D. C. source Es through charging resistor iii. In a like manner, three series paths of outer conductors are connected through leads 54, 55 and 12 to a common terminal 70 which is connected to the negative terminal of source Es. A normally open switch S1 is connected between terminals 64 and 70 to provide a conductive path between the inner conductor and outer conductor series paths upon closure thereof.

The operation of Fig. 4 is the same as for Fig. 3 except that the single pulse produced across load Z"1 is thrice the charging voltage of source E5 and has a duration twice the length of one of the coaxial lines.

From the foregoing, it is apparent that the invention provides a transmission line arrangement wherein collapse of an electrostatic field built up therein produces a pulse of rectangular configuration across a load.

It is also apparent that the invention provides an arrangement for producing pulses having a magnitude which is a multiple of the voltage from a charging source without distorting the wave form or continuity of the pulse.

It is further apparent that the invention provides a pulse generator which prevents the introduction of undesirable reactance and resistance etfects.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the teachings herein and the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In combination with a unidirectional current source of predetermined amplitude, a pair of terminals connected across said source, a plurality of dual line transmission systems of equal electrical length and characteristic impedances, circuit means including a load device interconnecting said systems in tandem to form a composite line, one of said dual lines of each transmission system being connected to have one of said pair of terminals in common, the other of said dual lines of each transmission system being connected to have the other of said pair of terminals in common, and circuit closing means connected across said pair of terminals for selectively discharging said composite line through said load.

2. An impulse generator comprising a source of direct current, a pair of terminals connected across said source, a pair of energy storing networks each comprising a corresponding number of coaxial lines, all of said lines being of equal electrical lengths and having equal characteristic impedances, circuit means including a load device interconnecting said networks to form a composite line, the impedance of said device being equal to the sum impedance of said lines, one conductor of each coaxial line and said load device being correlatively connected to form a first series circuit system, circuit means connecting one end of said first system to one of said pair of terminals, the other conductor of each coaxial line being correlatively connected to form a second series circuit system, circuit connections for connecting one end of said second system to the other of said pair of terminals, and circuit closing means connected across said pair of terminals for selectively discharging said composite line through said load to produce a pulse of uniform amplitude and preassigned duration thereacross.

3. The generator of claim 2, wherein said first and second systems each comprises a corresponding plurality of series paths extending from its respective one of said pair of terminals.

4. An impulse generator comprising a source of direct current, a load device, a first transmission line having a pair of spaced conductors connected across said source, a second transmission line having a pair of spaced conductors of which one is serially connected to one of said first mentioned conductors and the other is serially connected through said device to the other of said first mentioned conductors, and circuit closing means connected across said source for electrically connecting said first mentioned pair of conductors.

5. In a pulse generating system, a source of direct current, a pair of reflecting line type pulsing networks for storing electrical energy received from said source and proportioned to provide a pulse of uniform amplitude and preassigned duration, a load circuit electrically interposed between said pair of networks for connecting said networks in tandem to form a composite line, and a switching device connected across one end of said composite line and operable to discharge said networks across said load circuit, one of said networks including a plurality of coaxial lines having their inner conductors connected to one side of said source and their outer conductors connected to the other side of said source, said switching device being connected between said inner and outer conductors, the other of said networks including a plurality of coaxial lines having their inner conductors connected serially through the inner conductors of said one network to said one side of said source and their outer conductors connected serially through the outer conductors of said one network to said other side of said source.

References Cited in the file of this patent UNITED STATES PATENTS 

